He first worked as a casual employee of Dwight Heald Perkins and other architects in Chicago's Steinway Hall, then in 1901-06 as an associate of Frank Lloyd Wright at Oak Park. He also undertook private commissions, the most notable of which were the Emery house (1903) and the landscape designs for the grounds of the state normal schools of Eastern Illinois (1901) and Northern Illinois (1906). Griffin started his own practice in Steinway Hall in 1906 and by 1910, when his work was featured in the Architectural Record, was becoming recognized as a practitioner of what eventually became known as the Prairie School of architecture.

On 29 June 1911 Griffin married 40-year-old Marion Lucy Mahony (1871-1961), daughter of an Irish-born schoolteacher. They had no children. Tall, with a tomahawk profile and theatrical demeanour, she was the second woman to graduate in architecture from the Massachusetts Institute of Technology, in 1894. Wright, with whom she worked until 1909, had a high regard for her talents as a draughtsman, illustrator and designer of furnishings. After Wright absconded to Europe with Mrs Cheney, Marion joined the office of Hermann von Holst, with responsibility for Wright's uncompleted commissions. Her hero-worship of Wright was transferred to Griffin.

They were married two months after the international competition for the design of the new Federal capital of Australia was announced. Assisted by others in Steinway Hall, including Roy Alstan Lippincottâ??who soon married Griffin's sister, Genevieveâ??and George Elgh (all of whom joined the Griffins in Australia in 1914), Marion produced the elegant set of drawings illustrating Griffin's ideas. He won the competition in May 1912. She later claimed that it was only her importunings that persuaded him to complete the design, a grandly conceived arrangement for a national capital of 75,000, by the time required. Taking advantage of the topography within and around the splendid site, the plan was a masterly derivation fromâ??and an extension ofâ??the design ideas which Griffin had observed in the Chicago Fair (1893), the McMillan plan for Washington (1901), the Burnham and Bennett plan for Chicago (1909) and other work of their principal author, the Chicago architect Daniel Hudson Burnham, an outstanding figure in the City Beautiful movement.

Griffin and his winning design generated prolonged and bitter controversies. King O'Malley, the fustian minister for home affairs, appointed a reviewing board of departmental officers who produced their own plan, a grotesque scheme that was widely condemned. In 1913 after the fall of the Fisher government, William Kelly, acting minister for home affairs, invited Griffin to consult with the board. Kelly was completely won over by Griffin's missionary zeal and in October had him appointed Federal capital director of design and construction, a half-time post, for three years. The terms of the contract, drawn up by Griffin himself and intended to place him in effective control, were humiliating to the officers of the former departmental board, in particular the chairman, Colonel David Miller, head of the Department of Home Affairs and Lieutenant-Colonel Percy Thomas Owen, director-general of Commonwealth works. Believing that many features of Griffin's plan were vastly extravagant and incapable of realization, they nevertheless pressed on, to Griffin's chagrin, with the design and construction of the engineering works to serve the future city. In September 1914 when the Fisher government returned to power, another new minister, William Archibald, baffled by having to deal with 'two staffs of experts', demanded from Griffin, whom he described as a 'Yankee bounder', his long-promised 'amended plan', which was presented in March 1915. That month the Parliamentary Standing Committee on Public Works rejected Griffin's peculiar proposals for the sewerage system, and in November 1916 his extensive lakes scheme was rejected in favour of the more feasible proposals recommended by Owen. Griffin's railway proposals were not opposed, but no railway through the city was ever built.

The return of O'Malley as minister for home affairs under Billy Hughes in October 1915, this time as a friend and ally, had improved Griffin's prospects. In April 1916 O'Malley persuaded cabinet to renew Griffin's contract for a further three years. With O'Malley's connivance, William Webster, the postmaster-general, made a virulent attack in parliament on the officers responsible for the project. A royal commissioner, Wilfred Blacket, K.C., was appointed to inquire. For seven months from July 1916 Webster himself conducted what amounted to a case for the prosecution; Owen was, perforce, counsel for the defence. The commissioner's findings, presented in six reports in March and April 1917, were more remarkable for their discursiveness than their prudence. Blacket held Griffin blameless and found the former minister, Archibald, and certain unnamed officers guilty of forming 'a combination â?¦ hostile to Mr Griffin and to his design for the city'. He judged that many engineering decisions on water supply and sewerage were wrong, and made scathing observations about inefficient management and wasteful expenditure. He held the extreme view that Archibald should have 'either cancelled Griffin's contract and reverted to the design of the Departmental Board, or else have allowed Mr Griffin's contract to be performed and his design carried out'.

Prime Minister Hughes and his new Nationalist government, more concerned with Australia's wartime problems, appeared unimpressed with Blacket's findings. The works branch of Home Affairs had already been made a separate Department of Works and Railways (with Miller as its permanent head) during the course of the inquiry and the political career of O'Malley, Griffin's strongest supporter, had ended with his electoral defeat in May 1917. That year Griffin had the survey of the main axial lines of the city completed and in 1918 produced his final plan, showing the lakes exactly as he wanted them. But apart from tree-planting, little work was carried out on the site in the remaining years of Griffin's directorship. By 1920, when the Hughes government was importuned to meet the constitutional requirement to establish Canberra as the seat of government, it had become apparent that by training and temperament Griffin could not fulfil the executive role required. Offered a place on the Federal Capital Advisory Committee under the chairmanship of (Sir) John Sulman, he printed a resounding statement of the reasons for his refusal and circulated it, with copies of the findings of the Blacket commission, and his correspondence with the prime minister, to newspapers and periodicals throughout Australia.

The Sulman committee was instructed by the minister for works, Littleton Ernest Groom, to proceed 'on the basis of the acceptance of the plan of the lay-out of the Federal Capital by Mr W. B. Griffin'. In 1925, when an independent Federal Capital Commission was established with (Sir) John Henry Butters as chairman (and Owen as its chief engineer), Groom, then attorney-general, introduced the requirement that Griffin's plan should be published in the Government Gazette, and any variation to it be open to disallowance by parliament. In 1928 Griffin asserted that the commission 'had violated the aesthetic, social and economic principles in almost every act and [his] details for roads and services had not even been referred to in the actual work'. But Griffin's ideas were respected to the extent that they were judged feasible. The lakes scheme, as completed in 1964, designed without regard to the conflicts of fifty years before, conforms closely to the proposals of the otherwise discredited board's plan.

Throughout his seven turbulent years as part-time Federal director Griffin was active in private practice: for three years from 1914 in a long-distance Chicago partnership with Francis Barry Byrne, a former Oak Park colleague; until June 1915 in a short-lived partnership with John Burcham Clamp in Sydney; and from 1915 in his own office in Melbourne, with Marion, Lippincott and Elgh, who was soon to be replaced by an Australian, Edward Fielder Billson. Griffin's letterhead from that time carried the legend, 'Architect and Landscape Architectâ??Sydney-Melbourne-Chicago'. He undertook numerous site-planning commissions in the United States and Australia, only a few of which were carried out. The most notable were the Rock Crest-Rock Glen community in Mason City, Iowa, where Griffin designed some distinguished houses, the town plans for Griffith and Leeton, New South Wales, and the Summit and Glenard estates at Eaglemont, Melbourne. At Eaglemont the Griffins built the only house designed for themselves, a modest 'one-room' dwelling constructed in Knitlock, a precast concrete building block, which Griffin had patented in 1917.

In 1920 Griffin formed the Greater Sydney Development Association Ltd to build residential estates on three picturesque headlands on Sydney's Middle Harbour. The first estate, Castlecrag, designed to retain the character of the natural landscape, was begun in 1921 with several of Griffin's distinctive houses of rock and concrete intended to demonstrate the style of house lot-purchasers would be required to build. Although revered by later generations, the houses at the time were widely regarded as eccentric; they tended to leak. By 1937 only nineteen houses, sixteen of them designed by Griffin, had been built on the 340 lots. Griffin moved from Melbourne to Castlecrag in 1924, and his junior partner, Eric Milton Nicholls, followed in 1932. From 1929 the partnership survived almost entirely on commissions for the design of municipal incinerator buildings for the Reverberatory Incinerator & Engineering Co. Twelve were completed in the four eastern States. All were of distinctive design and two have been preserved by conversion; one near Castlecrag is a restaurant, another at Ipswich, Queensland, a community theatre.

Marion throughout encouraged Griffin in the role of a missionary, claiming the divine right of the gifted designer to have his own way. From time to time she produced superbly presented decorative drawings, colour-rendered on fabric, of his building designs; but her principal role at Castlecrag was as a community leader, organizing a variety of cultural activities from ballet classes to classical drama, staged in a rock-gully adapted to serve as an amphitheatre. Both Walter and Marion were interested in Theosophy until, in 1930, they were attracted to Anthroposophy, Rudolph Steiner's science of the spirit, which Marion extended to highly personal forms of mysticism.

Griffin was invited to design a library for the University of Lucknow and left for India in October 1935. Nothing came of this project but he was engaged as the designer of the United Provinces Exhibition of Industry and Agriculture in Lucknow and ran into troubles similar to those he had encountered with Canberra. Only a small part of his imaginative and extravagant scheme was carried out. But he and Marion were entranced by India and enthusiastically worked together on numerous designs for palaces and bungalows. Few of them were used, but one building commissioned to house the Pioneer newspaper was completed after his death.

Griffin died of peritonitis on 11 February 1937 in Lucknow five days after an operation, and was buried there. Marion, dissuaded from an attempt to carry on his work in India, returned briefly to Castlecrag where it was established that Griffin had left heavy debts. While unsuccessfully attempting to practise in Chicago, she wrote a disjointed account of her life with Griffin. The book-length typescript, 'The Magic of America', is in four parts, 'The Empirial [sic] Battle' (India), 'The Federal Battle' (Canberra), 'The Municipal Battle' (Castlecrag) and the 'Individual Battle'. It unwittingly helps to explain how her influence contributed to the difficulties Griffin had in his dealings with people and why he remained an expatriate.

Although at the time of his death Griffin might have been judged a failure, later generations regard his designs and ideas with a respect which would have astounded his contemporaries, and his surviving buildings are valued as part of Australia's architectural history. In 1963, the fiftieth anniversary of the naming of Canberra, a commemorative postage stamp was issued with his portrait. The Canberra lake, built in the form to which he was so strongly opposed, was given his name in 1964. A competition for the design of a memorial, on Mount Ainslie overlooking the city, to mark the centenary of his birth was won by an American entry, but following a change of government in 1975, and with strong echoes of similar changes fifty years earlier, the project was 'deferred'.